Introduction
Some time ago I have decided to try to make
something like a "Photoshop" in C#. The first problem has appeared was custom
cursors. If you are familiar with "Photoshop" you know that when you change
brush size the cursor size also changes. This is solution to make this possible
in C# . Note: hare will described only black and white cursors. It is possible
that I will upgrade this article or create new for 32-bit cursors.
Standard realization of class Cursor
practically completely repeats Win API for the cursor except for method
CreateCursor . This method is necessary for drawing custom cursor. So
we import it from library user32.dll.
[DllImport("user32.dll")] private static extern IntPtr CreateCursor( IntPtr hInst, int xHotSpot, int yHotSpot, int nWidth, int nHeight, byte[] pvANDPlane, byte[] pvXORPlane ); The method needs handle to the current window, coordinates of the cursor's hot spot, the size and mask of the image.
The sizes of the cursor :
Win API contains method
GetSystemMetrics which returns the possible size of cursor, but it
always return 32/32 for standard video devices or 64/64 for hi-resolution
devices. In the experimental way I have find out that the sizes of the cursor
should be multiple 16 px. So we will not use GetSystemMetrics .
Attempt of use of the non-standard size leads to wrong display of the image. As
greater accuracy is necessary for us than 16 px we shall take the size of the
cursor with a stock. All that remains will be in visible so this is for us!
Masks of the cursor:
The image of the cursor is set by means of two
masks (AND and XOR masks). Masks consist from array of byte where every b i t
designates one pixel. Here results of a combination of two pixels:
Result code:
Using CreateCursor function
this is simple to create new cursor from masks:
byte[]
andMaskCursor = new byte[]
{
0xFF, 0xFC, 0x3F, 0xFF, // line 1
0xFF, 0xC0, 0x1F, 0xFF,
// line 2
0xFF, 0x00, 0x3F, 0xFF,
// line 3
...
0xFF, 0xC3, 0xFF, 0xFF,
// line 31
0xFF, 0xFF, 0xFF, 0xFF
// line 32
};byte[]
xorMaskCursor = new byte[]
{
0x00, 0x00, 0x00, 0x00,
// line 1
0x00, 0x03, 0xC0, 0x00,
// line 2
0x00, 0x3F, 0x00, 0x00,
// line 3
...
0x00, 0x00, 0x00, 0x00,
// line 31
0x00, 0x00, 0x00, 0x00
// line 32
};IntPtr cursorHandle = CreateCursor(
handle,
// app. instance
radius,
// hot spot horiz pos
radius,
// hot spot vert pos
sideLength,
// cursor width
sideLength,
// cursor height
andMaskCursor,
// AND mask
xorMaskCursor
// XOR mask
);Cursor.Current = new
Cursor(cursorHandle);
Huuh.
. now we can create cursors programmatically .
Masks now are hard coded that is not applicable for us! Lets create mask with
circle cursor: int sideLength
= radius*2;
if
(sideLength%16 != 15)
{
sideLength = sideLength +
16-sideLength%16;
}
int length =
sideLength*sideLength/8;
byte[]
andMaskCursor = new byte[length];
byte[]
xorMaskCursor = new byte[length];
for (int
i = 0; i < sideLength; i++ )
{
for (int
j = 0; j < sideLength; j++ )
{
double x = i -
radius;
double y = j -
radius;
double pRadius
= Math.Pow(
Math.Pow(x, 2) + Math.Pow(y, 2), 0.5
);
if ((int)pRadius
!= radius)
{
int ii =
(i*sideLength)+j;
andMaskCursor[ii/8] =
(byte)Math.Pow(2,
7-ii%8);
}
}
}
That's all! Enjoy.